The U.S. military uses a family of 40 mm ammunition which includes high explosive grenades and various star and parachute illumination pyrotechnics—in white, green and red for illumination and signal purposes. More specifically, such illumination and signals are useful both day and night, to communicate a prearranged message, provide a beacon for rescuers, or to disclose, or illuminate the positions of military units or personnel. Such rescue or attention—getting applications are common in non-military situations, as well as, in military combat and training scenarios—the illuminant being shot at about 250 fps to a burst height of about 600 feet. Generally, these pyrotechnic illuminants contain significant amounts of potassium perchlorate (KClO4), a strong oxidizing material—which exothermically transfers oxygen to combustible materials, to provide pyrotechnics with a significant rate of combustion in air. However, KClO4 contaminates groundwater and impacts public drinking water. In particular, KClO4 interferes with hormonal regulation of the thyroid gland, and is known to be teratogenic. Accordingly, the U.S. Environmental Protection Agency has established a permissible KClO4 level at 15 parts per billion, and various states have mandated even lower levels, e.g. California has mandated no more than 6 parts per billion and Massachusetts has mandated only 2 parts per billion. In response, the U.S. Department of Defense is spending billions of dollars annually on perchlorate remediation efforts.
Colors in illuminating pyrotechnics are obtained by the addition of specific ingredients, which offer the desired flame color. For example, green is obtained with the addition of barium nitrate, which acts as both a color agent and an oxidizer. Similarly, strontium nitrate provides intense red and also acts as an oxidizer. The corresponding light emitting species (in the gas phase, during flaming) are the monohydroxides, SrOH and BaOH, and the monochlorides, SrCl and BaCl, for red and green. Therefore, as stated above, commonly in red or green pyrotechnics, potassium perchlorate (KClO4) is used—as, a chloride ion and hydroxide ion donor, which also is a strong oxidizer.
One 40 mm parachute deployed illuminant of particular interest is the U.S. Army red signal/illuminating device; the M662 parachute. The KClO4-containing in-service M662 red signal/illuminating pyrotechnic formulation (see Table 1, below) has a burn time of about 40 seconds, a minimum luminous intensity of about 19,000 candela, a dominant wavelength of 607 nanometers and a spectral purity of about 86.8%. This red military illuminant device is housed within a 40 mm hollow aluminum body, and as stated above, is fired to a height of about 600 feet, and floats back to earth suspended from a parachute—providing the desired red illumination or signal as it floats downward.
TABLE 1Current M662 red signal/illuminating pyrotechnic material.IngredientWeight PercentageStrontium Nitrate (Sr(NO3)2)41.1Magnesium 30/5030.8Polyvinyl Chloride (PVC)12.8Potassium Perchlorate (KClO4)10.3Laminac 4116/Lupersol Binder System5.0
As stated above, KClO4 acts as an oxidizer, and is so used in the current M662 parachute illuminant; where, with a second oxidizer, strontium nitrate (Sr(NO3)2), the KClO4 reacts with magnesium 30/50, an inorganic metallic fuel, to produce magnesium oxide (MgO). MgO is a gray body emitter, and is responsible for producing the necessary illumination intensity desired for the parachute illuminant (intensity measured in candela). Further, the reaction of the strontium atom with the chloride donor from another ingredient, polyvinyl chloride (PVC), will produce strontium (l) chloride (SrCl). SrCl is responsible for imparting the intense red color within the pyrotechnic material, though the strontium reacting with the oxidizer to produce strontium monohydroxide (SrOH) also contributes to the red emission. An organic-based/binder, usually Laminac 4116/Lupersol, mitigates the sensitivity and prevents separation of the oxidizer, fuel and chloride donor. And, finally, the resulting pyrotechnic material exhibits a good insensitivity to electrostatic discharge and a fair insensitivity to impact—but, only a moderate insensitivity to friction initiation.
Disclosed by Sabatini et al, Propellants, Explosives, Pyrotechnics, “Applications of High-Nitrogen Energetics in Pyrotechnics: Development of Perchlorate-Free Red Star M126A1 Hand-Held Signal Formulations with Superior Luminous Intensities and Burn Times,” August 2011, Vol. 36, Issue 4, pp. 373-378 (Wiley-VCH Verlag GmbH & Co., KGaA, Weinheim), available online at: http://onlinelibrary.wiley.com/doi/10.1002/prep.201000061/pdf, is an alternative to KClO4 based illuminant formulations for use in hand held signal (HHS)—which is similar to the subject 40 mm parachute illuminant—but, fired from a hand held tube. This alternative to KClO4 based formulation involves the use of an organomemetallic salt, with a strontium core and two nitro groups, i.e. strontium bis-(1-methyl-5-nitriminotetrazolate) monohydrate—a high energy, high nitrogen fuel. While a synthesis of strontium bis-(1-methyl-5-nitriminotetrazolate) monohydrate is disclosed in an article by Thomas M. Klapötke et al., Propellants, Explosives, Pyrotechnics, “Coloring Properties of Various High-Nitrogen Compounds in Pyrotechnic Compositions,” June 2010, Vol. 35, Issue 3, pp 213-219 (Wiley-VCH Verlag GmbH & Co., KGaA, Weinheim), use of such a synthesis is not amenable to mass, economic production and strontium bis-(1-methyl-5-nitriminotetrazolate) monohydrate is not commercially available.
More recently, another alternative red pyrotechnic illuminant was proposed by the inventors of the subject invention—again replacing the KClO4 based illuminant—with 5-aminotetrazole (5-AT) as the primary oxidizer and using the same secondary strontium nitrate (Sr(NO3)2) oxidizer and the same magnesium 30/50 inorganic fuel and grey body emitter. However, this 5-AT alternative also suffered from the same lack of commercial availability as does the previously discussed strontium bis-(1-methyl-5-nitriminotetrazolate) monohydrate alternative.
Clearly, there is a need in the art for a commercially available, economical, environmentally friendly, and non-toxic alternative to KClO4 in red pyrotechnic illuminant compositions, especially for use in 40 mm parachute devices and where the material provides a significant increase in insensitivity to friction initiation—i.e. increase in safety.